1. Field of the Invention
The present invention relates to an image reading apparatus for reading an image of a document, and more particularly to an image reading apparatus having an auto document feeder.
2. Description of the Background Art
Reading images is a process employed by various kinds of apparatuses such as image scanners, copying machines, facsimile machines, and so forth, which handle image data of a document. This process of image reading is generally performed by an image reading apparatus.
A background image reading apparatus includes an image reading unit for reading images and an auto document feeder which feeds a document to the image reading unit one sheet at a time from a number of sheets stacked. The auto document feeder is swingably mounted to an upper surface of the image reading unit to form a clamshell-like shape. With this configuration, the auto document feeder is allowed to be both lifted to an open position and lowered to a closed position.
When the auto document feeder is at the open position, it provides an access area to a book exposure glass of the image reading unit on which a document including a book document can be placed manually by an operator. In this operation, the auto document feeder is inoperable. When the auto document feeder is then closed down on the book exposure glass, it holds a document placed at a book reading position on the book exposure glass so that a book reading may be started.
On the other hand, a sheet reading using the auto document feeder may be ready to start when the auto document feeder is located at the closed position. In this operation, sheets to be read are stacked in the auto document feeder and are consecutively fed one after another to a sheet reading position on a sheet exposure glass of the image reading unit by the auto document feeder.
In the sheet reading, a sheet to be read is transported to pass through a gap of the sheet reading position formed between the sheet exposure glass and a bottom surface of the auto document feeder situated at the closed position. This gap of the sheet reading position needs to be accurately formed to perform an accurate image reading.